Mauro Iuliano

The hydrolysis of the La(III) ion in aqueous perchlorate solution at 60°C

Abstract The hydrolysis equilibria of the La(III) ion have been studied at 60°C by measuring, with a glass electrode, the hydrogen ion concentration of a series of lanthanum perchlorate solutions. The [La(III)] of the test solutions, which were made to contain 3 m (molal) C10 4 − by adding LiClO 4 , varied from 0.03 to 1 m. Hydrolyzed solutions were prepared by generating OH − by constant-current coulometry. The potentiometric data, which indicate that at most 3% of the metal ion can be transformed to reaction products without the formation of a precipitate, can be explained by assuming the mononuclear LaOH 2+ ion and the polynuclear La 2 OH 5+ , La 2 (OH 3 3+ and Le 3 (OH) 3 6+ ions. Their formation constants in the inert 3 m LiClO 4 medium are reported and the effects of medium changes, caused by the replacement of Li + with La 3+ , estimated by the specific interaction theory.

Fluorosilicate equilibria in acid solution

Abstract The reaction between silicic acid and the fluoride ion in aqueous solution has been investigated at 25°C in a 3 m (Li)ClO 4 medium, by potentiometric methods employing a fluoride ion-selective electrode to observe the free hydrogen fluoride concentration. The acidity varied between 0.3 and 3 m, while the concentration of silicic acid was maintained below 2.5 x 10 −3 m which is thought to be the saturation level of amorphous silica. The experimental data have been explained in terms of Si(OH) 3 F, SiF 4 , SiF 6 2− , HSiF 6 − and a minor species to which the composition Si(OH) 2 F + has been tentatively assigned.

Phosphato complexes of beryllium(II): a 31P and 9Be nuclear magnetic resonance study

Abstract 31 P and 9 Be NMR spectra of mixtures of beryllium(II) and phosphoric acid have been interpreted to support the speciation previously proposed on the basis of potentiometric measurements. Nine 31 P lines were observed at ≈0.4, −3.67, −4.51, −5.57, −6.5, −7.08, −8.81, −9.3 and −11.0 ppm relative to 85% phosphoric acid as external standard. The signal in the range 0.36–0.56 was assigned to rapidly exchanging H 3 PO 4 , H 2 PO 4 − with a further contribution from Be 3 O(H 2 PO 4 ) 6 2− . The peaks at −3.67 and −4.51 ppm were ascribed to isomers of Be(H 2 PO 4 ) 2 . The species Be(H 2 PO 4 ) + also gives a signal centred at −4.51 ppm. The peak at −6.5 ppm was assigned to Be 3 (OH) 3 (H 2 PO 4 ) 3 . The peaks at −5.58, −8.81 and −9.3 ppm are tentatively assigned to isomers of the complex Be 2 (OH)(H 2 PO 4 ) 2+ . Signals observed at −7.08 and −11.0 ppm could not be assigned to any of the complexes proposed by potentiometry. The 9 Be NMR data are also consistent with the model previously proposed.

Dioxouranium(VI) oxalate complexes

The complex formation between dioxouranium(VI) and oxalate ion has been investigated, at 25.00xa0°C, in 2 and 3 M NaClO4, by measuring the potentials of a glass and of a Hg2C2O4–Hg electrode. In the analysed solutions the upper limit of the uranium(VI) concentration did not exceed 0.03 M, the oxalate concentration was imposed by the modest solubility of its sodium salt in the ionic media (about 0.015 M in 3 M NaClO4) and the acidity was kept at levels higher than 0.01 M in order to hinder formation of hydrolysed and possible ternary species. The measurements have been interpreted by assuming the formation of mononuclear complexes only, according to the reaction UO22+xa0+xa0p C2O42−xa0⇌xa0UO2(C2O4)p(2xa0−xa02p)+. The equilibrium constants have been extrapolated to infinite dilution by applying the Specific Interaction Theory (SIT) and, in weight molarity (molality) units, are log 0β1xa0=xa07.38xa0±xa00.07, log 0β2xa0=xa011.72xa0±xa00.1, log 0β3xa0=xa013.6xa0±xa00.2. Under the same experimental conditions the protolysis constants of oxalic acid and several interaction coefficients, necessary for extrapolation of the results to the thermodynamic scale of activities, through the SIT, have also been determined.

Fluorogermanate(IV) equilibria in acid media

Abstract The equilibria between Ge(OH)4, HF and H+ ions in aqueous solution have been investigated, at 25°C in NaClO4 as well as in LiClO4 med The potentiometric data have been explained by the presence of GeF4, Ge(OH)F4−, GeF62−, HGeF6− and a minor complex to

An organouranium coordination polymer containing infinite metal oxide chains.

The title compound, catena-poly[[[dioxouranium(VI)]-bis(micro-2-hydroxybenzohydroxamato)] dihydrate], [[U(C(7)H(6)NO(3))(2)O(2)].2H(2)O](n), is a uranyl coordination polymer based on the salicylhydroxamate ligand. The ligand acts both as a chelate, forming five-membered rings, and as a bridge between two U atoms. The coordination around each U atom is a distorted hexagonal bipyramid. Infinite chains running along [001] are formed via bridging salicylhydroxamate O atoms. The chains have C(2) symmetry, with U atoms in special positions on twofold axes. The water molecules are not coordinated to the metal but crosslink, through hydrogen bonding, adjacent coordination polymer chains in the [110] and [110] directions.

Formation equilibria of tin(II) orthophosphate complexes

Abstract The complexation equilibria of Sn2+ ion with orthophosphate ions have been studied, at 25°C in 3 M NaClO4 ionic medium, by potentiometric titrations with Sn2+/Snue5f8Hg and glass electrodes. The concentrations of the metal and of the ligand ranged from 2.5×10−4 to 2.5×10−3 M and from 0.01 to 0.3 M, respectively. The hydrogen ion concentration varied between 0.1 and 10−5.8 M. The potentiometric data are consistent with the formation of the complexes: SnH2PO4+, Sn(H2PO4)2(aq), SnH2PO4HPO4−, SnHPO4(aq), Sn(HPO4)22−, Sn(HPO4)34− and SnPO4−. Stability constants for their formation in 3 M NaClO4 and in dilute solution are reported.

THE SOLUBILITY OF CALCIUM CITRATE HYDRATE IN SODIUM PERCHLORATE SOLUTIONS

The solubility, at 25°C, of calcium citrate, Ca3(C6H5O7)2. 4H2O, in NaClO4 solutions in the molality (m) range 0–3.5, has been determined by potentiometric titration with EDTA, using the Hg2+/Hg half-cell. The increase of solubility with m has been explained with the specific interaction theory by assuming, for Ca3(C6 H5 O7)2.4 H2 O(s) ⇄3Ca2+ + 26H55O7 3−, log Ks0= −17.81 ± 0.03 and the interaction coefficient between Na+ and C6H5O7 3− ions equal to 0.08 ± 0.03 −(0.06 ± 0.01)m. This coefficient allows the extrapolation to the infinite dilution reference state of stability constants determined in concentrated ionic media. Results of calculations compare well with those of the literature.

Protolytic equilibria in aqueous concentrated solutions of orthophosphates

Abstract The protolytic equilibria, in solutions prepared to contain 3 M Na+ ions by adding NaClO4, have been studied at 25°C by potentiometric methods using glass or hydrogen half-cells. Most of the experiments (glass electrode) have been carried out in Na(ClO4, H2PO4) media where the phosphate molar concentration ranged from 0.1 to 3. A few experiments (hydrogen electrode) have been made in Na(ClO4, HPO4) media at the phosphorus(V) levels of 0.3 and 1 M. The potentiometric data are consistent with the presence in solution of dimers, Hn(PO4)2n−6, with n ranging from 1 to 6, as well as of the usual monomeric species. The formation constants are found to vary significantly as orthophosphates replace ClO4− ions of the medium. This phenomenon is ascribed to strong short-range interactions of the polar H2PO4− and HPO42− ions with other species, even negatively charged ones, in evident contrast with the Bronsted principle.

Homocysteine disulphides and vascular disease.

The total plasma concentration of homocysteine is a marker of this amino acids atherogenic potential. However, the homocysteine pool exists almost entirely as oxidized homocysteine equivalents (OHcyE), composed of homocystine and cysteine-homocysteine disulphides (20–30%), and protein-bound disulphide (70–80%). We have noticed that the total concentration of OHcyE in injured coronary artery tissue is higher than the aqueous solubility of homocystine (∼1.4–1.5 × 10-3 mol kg-1 versus ∼0.6 mol kg^{-1}). Based on the measurement of the solubility of homocystine in a plasma-mimetic condition (0.17 mol kg^{-1} NaCl at 37°C), we have estimated that OHcyE may really reach their saturation limit in the vascular tissue (0.93–1.02 × 10-3 mol kg-1), above which their deposition as solid phase may occur. This means that significant leakage of intracellular fluid can promote OHcyE crystallization in tissue fluids, which may serve to initiate inflammation. We speculate that deposition of OHcyE crystals could damage blood vessels and act as a primer of homocysteine-triggered inflammation, thus being along the causal pathway that leads to vascular dysfunction.